Kind of like link exchanges, which I currently am not doing, is there a limit or safe amount to sumit per day??
Ive done $1500 in the past week on directories and always do the same for each new site i make. Ive never noticed any penalty now compared to when i didn't do it. I believe your time in the sandbox is far less if you submit to the right directories. But don't forget about other links as well, 100% directory links i wouldn't recommend but thats your choice.